IP Multimedia Subsystem (IMS) is a 3rd Generation Partnership Project (3GPP) standardised network architecture that provides an access network independent standardised interface for creating services, charging mechanisms and better Quality of Service (QoS) than best effort. Examples of the services that may be implemented on IMS are Instant Messaging (IM), IMPS (Instant Messaging and Presence Service), Simple/IM (SIP for Instant Messaging and Presence Leveraging Extensions/Instant Messaging). Instant message is a message delivered to a user in an instant, interactive manner. Generally short, even brief Instant Messages are often called IMs. IMs are often exchanged back-and-forth between users in a conversational fashion. In other words, it is a type of messaging service by which the sender expects immediate message delivery in (near) real time fashion. Instant Messaging using SIMPLE is defined in OMA-TS-SIMPLE_IM-V1—0-20070816-C.
The Short Message Service (SMS) has enjoyed great success in cellular networks. At the same time, specifications have been and are being developed for extending 3GPP services to non-cellular IP Connectivity Access Networks (IP-CANs). 3GPP TS 23.204 specifies how to deliver SMS over generic 3GPP IP access, where the Short Message (SM) is entirely encapsulated in the SIP based messages so that the traditional SM not only can be delivered in Circuit Switched domain (CS), but also in IMS over different IP-CANs. An IP-Short-Message-Gateway (IP-SM-GW) provides the protocol interworking for delivery of the short message between IP-based User Equipment (UE) in IMS and a Service Center (SC). The message is routed to the SC for delivery to the SMS-based user equipment or the message is received from the SC of an SMS-based UE for delivery to an IP-based UE.
However, the interworking between the Short Message and the Instant Messaging has not been defined yet, which prohibits the message interworking between the traditional SMS terminals and the non-SMS capable terminals. 3GPP TR 23.811 V1.2.1 (2008-02) discloses alternatives for how to provide a service level interworking for instance between short message (SM) and existing Instant Messaging (IM) services, which enables the communication between SMS terminals and the terminals that do not support the SMS, such as pure SIP terminals. It is responsible for converting the IM service to SMS and vice versa. It performs the conversion e.g. based on user preference and operator policy, i.e. when the UE is able to use both services, the policy or preference may define which service is used. It may also happen that the UE or the radio access network is capable for one service only, in which case the interworking function may need to perform the conversion to different service. This new interworking to support protocol interworking and translation between SMS and IM Messaging may be implemented in the IP-Short-Message-Gateway (IP-SM-GW).
Both IM and SM services define a delivery report mechanism. When a short message is sent, a service center SC or the recipient UE may send an SM status report or a delivery notification, which confirms the delivery of the short message to the recipient, or it may be a failure report, which informs the originator that the short message was never delivered and the reason why. Similarly, when an instant message is sent, a corresponding delivery notification of the IM service may be sent. When these delivery report messages are received at the service lever interworking function, such as at the IP-SM-GW, these messages are processed as any other message, e.g. they may be converted e.g. based on user preference and operator policy, i.e. when the UE is able to use both services, the policy or preference may define which service is used.
However, different messaging services may be implemented in independent, separate applications in the UE. This means that if the UE sends the actual message via SM service, it expects also the delivery report via that service. The same applies to IM service as well. If the delivery report comes to the UE via different service which was used to send out the actual message, the UE has no means to bind the delivery report to the actual message.
With the current IM-SMS interworking function, it may happen that a message and its delivery notification or status report are sent and received with different services: an SM status report is sent for an instant message (IM), or an IM delivery notification is sent for a submitted short message (SM). Let us study some examples of situations where this could happen. (i) UE sends an instant message (IM) while being registered to the IMS, but deregisters from the IMS before a delivery notification of the IM is sent back, thus the delivery notification is interworked to an SM status report. (ii) UE sends an instant message (IM), which is interworked to a short message (SM) according to operator policy, but the returning status report is not interworked. (iii) A message is sent as a short message (SM) (UE is not registered to the IMS), but the status report is interworked to an IM delivery notification according to user preferences.
Obviously, if an initial message and its delivery notification are handled by different applications in the UE, the UE cannot find the relation between these events. Thus, there is a need for avoiding or alleviating this problem.